<?php
	require_once "Categories.php"; 
	
	class MainCategories extends Categories 
	{
		public $subCatIds;
		
		public function MainCategories()
		{
			$this->subCatIds = array();
		}
		
		public function addCatId( $id )
		{
			array_push( $this->subCatIds, $id );
		}
	}	
	
	$mainCat = new MainCategories();
	
	$mainCat->addCatId( 120 );
	var_dump( $mainCat );
	
?>